290 Mr Jenyns's Monograph on the 



paper. Having for many years paid considerable attention to 

 this family, during which time I have not only increased the 

 list of British species, but have also endeavoured to ascertain the 

 extent of variation to which each of them is subject ; having 

 likewise been fortunate in obtaining authentic specimens of many 

 of those alluded to by British authors, I thought that it might 

 be rendering a service to the conchologists of this country, if 

 I were to throw together, in the form of a monograph, the 

 observations which I had made, and to draw up an amended 

 list of all the species hitherto detected in this island, accompanied 

 by full descriptions, and illustrated by magnified figures. In my 

 attempt to do this, I have not merely considered the general 

 characters of the shell, but in determining the species have de- 

 rived much assistance from attending to the animal inhabitant. 

 The species themselves are found in rivers, ditches, and streams ; 

 the smaller ones not unfrequently in the gullies that are cut in 

 pastures for the purpose of draining the soil : they all however 

 live readily in confinement for several days when kept in water ; 

 and under these circumstances their different habits may be con- 

 veniently observed. Occasionally it will be found that they be- 

 come languid and inert, especially if they have been confined 

 a long time; but they may generally be roused into activity by 

 the sudden application of cold spring water, and this is by far 

 the best method of getting a sight of the siphonal tubes, which 

 in some cases afford good distinguishing characters. Indeed it is 

 absolutely requisite to caution conchologists against drawing any 

 conclusions with respect to the specific distinction of these animals 

 from a mere inspection of the shell alone. This is so liable to 

 vary from age, peculiarity of situation, and probably from other 

 causes, that it becomes necessary in some cases to compare a 



